Since pentamidine has become commercially available, there is renewed interest in using it as the initial treatment for Pneumocystis carinii pneumonia (PCP) in AIDS patients. We reviewed the use of pentamidine in 24 patients with PCP to gain information on the prevalence and severity of adverse effects from this drug. Twenty out of twenty-four patients (83 percent) experienced some kind of adverse effect. Hepatic abnormalities (58 percent), nausea and vomiting (46 percent), hypoglycemia (33 percent), azotemia (25 percent), and pain at the injection site (25 percent) were the most frequently seen effects. We recommend monitoring guidelines to be applied during pentamidine therapy based on the observed frequency of specific side effects.